Compressed motor winding

ABSTRACT

In one possible implementation, a method for forming a motor winding is provided which includes compressing a Litz wire to form a compacted Litz wire and forming the winding with the compacted Litz wire. In one possible embodiment, a motor winding is provided that has a high density multi-conductor wire bundle comprises of compacted Litz wire.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the following applicationswhich are herein incorporated by reference in their entireties:

-   -   U.S. Provisional Application No. 61/194,098, filed Sep. 23,        2008, by Daboussi, entitled WINDING DESIGN FOR IRONLESS P.M.        MOTOR; and    -   U.S. Provisional Application No. 61/194,099, filed Sep. 23,        2008, by Daboussi et al, entitled PROPELLER DRIVE UNIT FOR HALE        UAV; and    -   U.S. Provisional Application No. 61/194,056, filed Sep. 23,        2008, by Hibbs, entitled FLUX CONCENTRATOR FOR IRONLESS MOTORS.

The present application is also related to the following applications,which are hereby incorporated by reference in their entireties:

-   -   U.S. Non-provisional application Ser. No. 12/565,715, filed Sep.        23, 2009, entitled MOTOR AIR FLOW COOLING, by Sheppard et al;    -   U.S. Non-provisional application Ser. No. 12/565,710 filed Sep.        23, 2009, entitled STATOR WINDING HEAT SINK CONFIGURATION, by        Daboussi et al; and    -   U.S. Non-provisional application Ser. No. 12/565,718 filed Sep.        23, 2009, entitled FLUX CONCENTRATOR FOR IRONLESS MOTORS, by        Hibbs et al.

BACKGROUND

Electric motors for vehicles need to have high efficiency to conservepower. Furthermore, in vehicles, and in particular in aerial vehicles,light weight and compact electric motors are also desirable. Thus,ironless motors are often used which can provide the benefit of no ironlosses due to changing flux direction.

Motors are normally rated for the peak power and efficiency of themotor. In some applications, high part load efficiency is desired, whichis high efficiency when machine is loaded at a partial load, i.e. 15% orsome other percent.

What is needed is a higher efficiency compact motor.

SUMMARY

In one possible embodiment, a motor winding is provided that has a highdensity multi-conductor wire bundle comprised of compacted Litz wire.

In one possible implementation, a method for forming a motor winding isprovided which includes compressing a Litz wire to form a compacted Litzwire and forming the winding with the compacted Litz wire.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be betterunderstood with regard to the following description, appended claims,and accompanying drawings where:

FIG. 1 shows a simplified exploded perspective view of an example motor.

FIG. 2 shows a simplified cross-sectional side view of the motor of FIG.1 along its longitudinal axis.

FIG. 3 shows a simplified perspective view of the stator having awinding.

FIG. 4 shows a simplified cross section of the stator of FIG. 3.

FIG. 5 shows a simplified cross section of a Litz wire bundle.

FIG. 6 shows a simplified cross section of compacted Litz wire bundle.

FIGS. 7 and 7A show a simplified example of a plain winding in top andcross sectional views, respectively.

FIG. 8 is a simplified illustration of a non-woven three phase winding.

FIG. 9 is a simplified illustration of a woven three phase winding.

FIG. 10 is a simplified illustration of a two-layer winding.

FIG. 11A is a simplified top view of an example wire bending tool.

FIG. 11B is a simplified side view of a mandrel of FIG. 11A along the11B-11B line of FIG. 11A.

FIGS. 12A and 12B show simplified top views of bending jigs.

FIGS. 13 and 14 show simplified top views of bending jigs illustratingalternate implementations for reversing the direction of the wires.

FIG. 15 shows a simplified perspective view of a pressing tool.

FIG. 16 shows a perspective view of a bent Litz wire after compacting inthe pressing tool of FIG. 15.

FIG. 17 shows a top view of woven compacted Litz wire.

DESCRIPTION

FIG. 1 shows a simplified exploded perspective view of an example motor10 along axis 22. A stator 40 is secured to a housing 60. Inner rotor 50and outer rotors 30 are secured to each other and surround the stator40. An optional propeller hub 75, into which propeller blades 70 aremounted, is secured to the inner rotor 50. The propeller hub 75rotatably mounts on the spindle 65 with bearings 16 and 18. The bearings16 and 18 are retained by retainers 20 and 14 and cover 12.

FIG. 2 shows a simplified cross-sectional side view of the motor 10 ofFIG. 1 along its longitudinal axis 22. The stator 40 is located betweenmagnets 35 and 55 of the inner and outer rotors 50 and 30, respectively.The propeller hub 75 is bonded to the inner rotor which is rotatablymounted on the spindle 65. The spindle 65 may be fabricated of carbonfiber or other suitable material.

FIG. 3 shows a simplified perspective view of the stator 40 having awinding 45. The winding 45 is encased within the stator 40. Cooling fins42 and 44 are bonded to the front and back stator yoke portions 43 f and43 b, respectively.

FIG. 4 shows a simplified cross section of the stator 40 of FIG. 3. Thewinding 45 has a compressed central region 45 c. The winding 45 iscompressed in the central region 45 c so that more conductor material ofthe winding 45 can be placed between the magnets 35 and 55 (shown inphantom line) and so that more conductor can be located closer to themagnets 35 and 55 of the rotors 30 and 50 to provide increased magneticfield strength in the winding 45. In this embodiment, it is notnecessary that the ends 45 e of the winding 45 also be compressed. Thisis because the ends 45 e of the winding 45 do not pass between themagnets 35 and 55 of the rotors 30 and 50.

In accordance with various embodiments, for both axial and radialironless P.M. or permanent magnet machines, the winding 45 should have ahigh packing density to minimize I²R losses and a construction thatminimizes eddy losses. The magnets 35 and 55 in the rotor 30 and 50 passover/under a central active region 45 c of the stator winding 45, andnot over/under the edges 45 e of the stator winding 45. Thus, in variousembodiments, the active region 45 c of the winding 45 should have asmuch conductor, i.e. copper, as possible in the volume of the activeregion 45 c.

Also, in various embodiments, the winding 45 should have high rigidityso that the winding 45 does not deflect and contact the magnets 35 or55, and to adequately withstand the turn-to-turn voltages and associatedforces. The winding 45 is enclosed in a suitable material, such asepoxy.

For most embodiments, as excessive heat can damage the magnets 35 and55, the winding 45 should also have a low thermal impedance contact tothe peripheral yoke portions 43 f and 43 b so that heat is easilyremoved to inhibit excessive temperature rise within the motor 10. Invarious embodiments, the winding is encased in a thermally conductivematerial to transfer heat away from the winding 45 to the cooling fins42 and 44 via the front and back yoke portions 43 f and 43 b,respectively. Thus, in some embodiments, the winding 45 is encased inepoxy mixed with a thermally conductive filler such as aluminum oxide,boron nitride, or other material that promotes heat transfer.

Turning to FIG. 5, to minimize eddy losses, Litz wire 500 may be usedfor the winding 45 (FIG. 3). FIG. 5 shows a simplified cross section ofa Litz wire bundle 500. One source for Litz wire is New England WireTechnologies, of Lisbon, N.H., www.newenglandwire.com, which isdistributed by Cooner Wire company, in Chatsworth, Calif.,www.coonerwire.com. Litz wire 500 is a bundle of small conductor wires510, insulated 515 from each other, and braided. Litz wire 500 isbraided to allow each wire 510 to interact with the same averagemagnetic field over time, so that the same voltage develops across eachwire. This inhibits voltages and conduction between the individual wires510.

Turning to FIG. 6, in various embodiments, to further improveperformance, the Litz wire 500 of FIG. 5 is compacted as illustrated inFIG. 6. As shown in FIG. 5, the individual wires 510 are round so havespaces 520 between the wires 510. The compacted Litz wire 600 of FIG. 6,has greatly reduced spacing 620 between the wires 610. Thus, theconductor density is greater.

The compacted Litz wire 600 may be used to form the winding 45 (FIG. 3).The Litz wire 600, with multiple jacketed 615 conductors 610 aremutually twisted and compressed to produce conductors 610 having a crosssection that minimizes voids 620, i.e. rectangular cross sectionconductors 610. In one embodiment, Litz wire 500 (FIG. 5) having bundles500 of one hundred conductors 510 (FIG. 5) is used. A key parameter isthe “bundle pitch”—which is the length over which each bundle undergoesa complete 360 degree twist.

Turning to FIGS. 7 and 7A, which show simplified example of a plainwinding 745 in top and cross sectional views, respectively. For someembodiments, the bundle pitch should be equal to approximately twice theend 745 e turn length L_(et). When this relation is maintained, endturns 745 e can be formed with minimal distortion and the formingprocess is least difficult.

Typically, the wire 745 thickness (t) is less than the width (w). Assuch, a special bending jig is require which constrains the conductor“in plane” while the bend is applied.

FIGS. 11A and 11B are a simplified illustration of a possibleimplementation in a process for forming an embodiment of the winding.For both axial and radial designs, in some implementations the firststep is to force the Litz into a serpentine as shown in FIG. 7. Thus,for a 3 phase winding, at least three such conductors 745 must beformed.

To form the serpentine bundle 745 The Litz wire 500 is place on abending tool 1100, clamped, and bent. After bending, it is removed fromthe bending tool and placed in a press. The press compacts the centralregion 45 c of the Litz wire bundle 500 (FIG. 5) to provide thecompressed winding 600 shown in cross section in FIG. 6.

After bending and compressing, the compressed winding 845 a may be,combined with other similar compressed bundles 845 b and/or 845 c byoverlapping 845 as shown in FIG. 8, by weaving 945 as shown in FIG. 9,or layered 1045 as shown in FIG. 10, or with other patterns andcombinations of such.

Referring to FIGS. 8 and 9, for one winding embodiment, each pole has 1turn and the resulting winding is a single layer. For a three phasewinding, the three conductors can be “non-woven” and layered as shown inFIG. 8 or woven—as shown is FIG. 9. Shown in FIG. 8, the compacted Litzwire winding 845 b is placed in phase over compacted Litz wire winding845 a, then compacted Litz wire winding 845 c is placed over compactedLitz wire windings 845 b and 845 a. No weaving is applied in FIG. 8. InFIG. 9, the compacted Litz wire windings 845 a, 845 b, and 845 c arewoven into a single winding 945.

Embodiments with two turns per pole may be achieved via the techniquesof FIGS. 8 and 9, with six compacted Litz wire windings are used in theplace of three, but the winding may remain a single layer.

Alternatively, a two-layer winding 1045 can be used as shown in FIG. 10.The two-layers provide the winding 1045 the advantage of reduced endturn bulge and an increased end turn surface area. This aids heattransfer in various embodiments. In this embodiment, the windings 845 a₁, 845 b ₁, 845 c ₁, 845 a ₂, 845 b ₂, and 845 c ₂, are both woven andlayered in top and bottom layers such that the windings both weavebetween the other windings and between the top and bottom layers.

The layer scheme above can be extended by using increased numbers ofcompacted Litz wire windings having proportionately reduced widths. Withthis approach 4, 6 . . . 2n number of turns per pole can be achieved.

Referring to FIGS. 11A and 11B, forming tool 1100 allows you to startwith a straight wire and keep the central portions 1145 c straight whileforming the end turn bends 1145 et and to keep the wire 1145 aligned sothat it does not separate.

In addition to the serpentine bends, in various embodiments, the endturns 1145 et are twisted “out of plane” such that groups (eg. three)serpentine Litz wires 1145 can nest together. This allows the centralportions 1145 c to stack together more compactly, to reduce thethickness of the stator (FIG. 4) in the central portion 40 c (FIG. 4) sothat more conductor can be placed in the stator 40 and fit between themagnets 35 and 55 of the inner and outer rotors 30 and 50 (FIG. 2).

As discussed further below, the serpentine wire 1145 is compressed afterit is removed from the bending machine 1100. The end turns 1145 et maybe held within a forming tool when the center straight portions 1145 care compressed.

Referring to FIGS. 11A and 11B, in one implementation, after theserpentine bends are formed, the end-turns are twisted out of plane sothat wires can be nested/weaved together. FIG. 11A is a simplified topview of an example wire bending tool. FIG. 11B is a simplified side viewof a mandrel 1110 of FIG. 11A, along the 11B-11B line of FIG. 11A.

Turning to FIGS. 12A and 12B, in one implementation, to start bendingthe winding, a first mandrel 1210 is screwed into a first left hole atop row of a jig 1200. The jig 1200 has two rows of offset mandrel screwholes. The hole 1235 placement will vary depending on the width of thewire 1245, and the length and width of the magnets of the rotor(s). Asecond mandrel 1211 is screwed into the first left hole in lower row.The wire 1245 is inserted into, and extending between, the first andsecond mandrels. The first mandrel 1210 is tightened to hold the wire1245 in place.

While holding the start 1245 s of the wire 1245, insert U shaped guide1205 onto wire 1245 and form the wire 1245 around the second mandrel1211 by hand, pulling with about 25 pounds of force at the same timepulling U shaped guide 1205 around as indicated by arrow 1206 in FIGS.12A and 12B. In various embodiments, the wire 1245 is over bent untilthe wire 1245 touches first mandrel 1210.

Typically, the insulation surrounding the wire bundle 1245 will need tobe pulled, or smoothen out during/after each bend, as there will beexcess material leftover after each bend.

Insert a third mandrel (not shown), and so on, and continue the sameoperation until you reach a desired number of bends, for example 20bends. Alignment marks may be added to the centers, or elsewhere, alongwith the winding identification number on each section if the winding isto be weaved.

As the mandrels are removed a heat gun is used to heat each end turn,which is then cooled to hold the shape of the end turns after themandrels are removed. The bends may be slightly squeezed, to over bendwhile heating, to help maintain the shape of the end turns after the endturn is cooled.

After sufficient turns have been added to complete a perimeter for anannular winding, the direction of the wire is reversed so that it goesback on itself. There are two different methods that can be used toaccomplish this as illustrated in FIGS. 13 and 14.

FIGS. 13 and 14 show simplified top views of bending jigs 1200 and 1400,respectively, illustrating alternate implementations for reversing thedirection of the wires 1245 and 1445, respectively. As show in FIG. 14,the wire 1445 can be twisted 180 degrees, illustrated at 1445 t. Whenthere is limited space between the mandrels in the different rows, orthe Litz wire 1245 is relatively wide, the implementation of FIG. 13 maybe utilized.

Shown in FIG. 13, there are two holes for mandrels 1221 and 1222 thatare vertically in line, rather than offset or staggered. A mandrel 1222with a cut out (not shown) on the bottom (adjacent the jig surface 1200s) may be used to clear the last winding 1245 a, and may also clamp andhold the last winding 1245 a from moving.

Making two turns in the same direction puts stress on the wire 1245, soit is advantageous to place as much bend in the reversing turn aroundmandrel 1222, for example about 120 degrees, or more, around mandrel1222. The wire 1245 may then be loaded again at the front of the bendingjig 1200 to bend the second section. An alignment mark may be placed onthe wire 1245 before removing it from the mandrels 1221 and 1222 totransfer it to the front of the bending jig 1200.

After forming the coils but before braiding, the central straightportions 1145 c (shown in FIG. 11A) may be compressed with 15-25 tons,or more, in a press to form the compacted Litz wire 600 of FIG. 6. Theend turns 1145 et (shown in FIG. 11A) are not compressed with the 25 tonpress, but do have to fit within the epoxy mold to form the stator. Theepoxy mold does compress the ends turns 1145 et, but not so that itforms the compacted conductors 600 as shown in FIG. 6.

Turning to FIG. 15, shown is a simplified perspective view of a pressingtool 1500, which may be used to compress and straighten the centralstraight portion 1645 c in a hydraulic press 1550. Alignment marks maybe used to line up the center of the central straight portion 1545 cwithin the groove 1500 g in the pressing tool 1500. The top plate 1500 thas a rail or tongue 1500 r that fits in the groove 1500 g andcompresses the central straight portion 1545 within the groove 1500 g.In one embodiment, the pressing tool 1500 and press 1550 produce acompacted straight central portion 1645 c measuring approximately 0.09″thick (t) by no wider than 0.425″ wide (w), shown in FIG. 16. FIG. 16shows a perspective view a Litz wire 1645 after compacting in thepressing tool 1500 of FIG. 15.

Alignment marks may be place on the wire while in the pressing tool1500, or after compression to indicate the compressed central straightportion 1645 c to facilitate weaving.

The compacted Litz wire 600 (FIG. 6), ends up having higher packingdensity than the original. It minimizes the gaps between the individualwires within the Litz wire 600 (FIG. 6). This compacted Litz wire hasgreater density so that more copper can fit between the stator androtor. Further, because the wire has planar surface it stacks togetherbetter when braided so can be placed closer together, and the braidedstructure can be located closer to the magnets across the air gap.

Referring to FIG. 17, after the Litz wire bundle is compacted, the Litzwire bundles may be weaved with other Litz wire bundles. Bent andcompacted Litz wire bundles are place in shuttles (not shown), orsleeves, for weaving on an alignment jig 1700. When weaving threewindings, vertically orienting the shuttles (not shown) and windingstherein, with number 4 winding in front, then number 5 and number 6,then number 1, number 2, and number 3 in back facilitates weaving, insome implementations.

FIG. 17 shows and end reversing turns 1745 e for three wires 1745 a,1745 b, and 1745 c. The wires 1745 a, 1745 b, and 1745 c can be markedwith numbers during the bending for use in the braiding, for examplewinding 1745 a may be marked as number 1 on one side and the secondsection (after the reversing turn) as number 4. Second coil 1745 b willbe number 2 and number 5, third coil 1745 c number 3 and number 6.

The alignment jig 1700 aligns the Litz wires during the weaving processso that turn pitch is accurately defined. Lay the turnaround winding inthe first 3 slots on the alignment jig 1700 making sure they arecentered. Then lay windings 1, 2 and 3 in the next three slots. Thenweave by picking up the shuttle with number 4 and move to the rear ofthe stacks. Insert the number 4 winding over the number 1 winding thenthe next number 4 turn in the empty slot next to the number 3 winding.Next move shuttle number 5 to the rear, then the number 5 wire turn laysover the number 2 wire turn, and the next number 5 wire turn is placedin the slot next to the number 4 wire, and so on.

To hold the wires 1745 a, 1745 b, and 1745 c from moving, place thenylon tubes (not shown) over, or between, each tang 1776 as the wires1745 a, 1745 b, and 1745 c are weaved.

The woven compacted Litz wire is stitched with material, such as lacingcord, so that end turns are locked together and so that the completedwinding can be handled after removal from alignment jig 1700. Forexample, there may be four lacings total, one on each edge for the endturns, and one on either side of the central compacted region.

Clean the braided and laced winding with acetone or alcohol and removeit from the alignment tool 1700 and place it on a steel hoop (not shown)to support the braided and laced winding when loading it into the epoxymold (not shown). Wrap the braided and laced winding around the hoopwith the numbers facing out and the last 3 turnaround coils laying ontop of the 3 finish turns 6, 5 and 4 so that the start and finish are inthe same plane.

Secure the braided and lace winding to the hoop with a nylon strap (notshow). Tighten the strap until the coil is uniform and the free ends arein line in the same plane and lace the free ends with lacing cord, Besure the central compressed active regions do not overlap are alignedproperly.

Thermistors may be added in various locations, including where the turnaround coils meet the free ends.

After the winding is laced, it is put into a mold and epoxied. For anaxial winding, a two-part (clamshell) mold can be used to epoxy thestitched winding. For a radial winding, a six-part mold is prossible.This includes one inner diameter mold, three-piece outer diameter molds,and two face molds. The potting material should be thermally conductiveepoxy type resin. For example, epoxy doped with boron nitride. Boronnitride as filler, although more expensive, is lighter than aluminumoxide, so better for aerospace applications.

The stator yoke portions 43 f and 43 b (FIGS. 3 and 4) and cooling fins42 and 44 (FIGS. 3 and 4) are attached to the ends 40 e (FIG. 4) of thestator 40 after it is the winding has been epoxied.

It is worthy to note that any reference to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment may beincluded in an embodiment, if desired. The appearances of the phrase “inone embodiment” in various places in the specification are notnecessarily all referring to the same embodiment.

The illustrations and examples provided herein are for explanatorypurposes and are not intended to limit the scope of the appended claims.This disclosure is to be considered an exemplification of the principlesof the invention and is not intended to limit the spirit and scope ofthe invention and/or claims of the embodiment illustrated.

Those skilled in the art will make modifications to the invention forparticular applications of the invention.

The discussion included in this patent is intended to serve as a basicdescription. The reader should be aware that the specific discussion maynot explicitly describe all embodiments possible and alternatives areimplicit. Also, this discussion may not fully explain the generic natureof the invention and may not explicitly show how each feature or elementcan actually be representative or equivalent elements. Again, these areimplicitly included in this disclosure. Where the invention is describedin device-oriented terminology, each element of the device implicitlyperforms a function. It should also be understood that a variety ofchanges may be made without departing from the essence of the invention.Such changes are also implicitly included in the description. Thesechanges still fall within the scope of this invention.

Further, each of the various elements of the invention and claims mayalso be achieved in a variety of manners. This disclosure should beunderstood to encompass each such variation, be it a variation of anyapparatus embodiment, a method embodiment, or even merely a variation ofany element of these. Particularly, it should be understood that as thedisclosure relates to elements of the invention, the words for eachelement may be expressed by equivalent apparatus terms even if only thefunction or result is the same. Such equivalent, broader, or even moregeneric terms should be considered to be encompassed in the descriptionof each element or action. Such terms can be substituted where desiredto make explicit the implicitly broad coverage to which this inventionis entitled. It should be understood that all actions may be expressedas a means for taking that action or as an element which causes thataction. Similarly, each physical element disclosed should be understoodto encompass a disclosure of the action which that physical elementfacilitates. Such changes and alternative terms are to be understood tobe explicitly included in the description.

Having described this invention in connection with a number ofembodiments, modification will now certainly suggest itself to thoseskilled in the art. The example embodiments herein are not intended tobe limiting, various configurations and combinations of features arepossible. As such, the invention is not limited to the disclosedembodiments, except as required by the appended claims.

What is claimed is:
 1. A method for forming a motor winding comprising: a) compressing a bundle of Litz wire to form a bundle of compacted Litz wire; b) forming a winding comprising the bundle of compacted Litz wire after compressing the Litz wire; and c) bending the bundle of Litz wire into a serpentine configuration prior to compressing the bundle of Litz wire; and d) wherein bending the bundle of Litz wire into a serpentine configuration comprises forming the serpentine configuration with central portions and end turns, and wherein compressing comprises separately compressing each of the central portions prior to forming the winding.
 2. The method of claim 1, further comprising combining multiple bundles of compacted Litz wire.
 3. The method of claim 2, wherein forming the winding comprising forming an annular winding after bending, compressing, and combining the multiple bundles of compacted Litz wire.
 4. The method of claim 3, wherein forming the winding comprises encasing the winding in a thermally conductive epoxy comprising boron nitride.
 5. The method of claim 1, wherein bending the Litz wire into a serpentine configuration comprises forming the winding with a central portion and end turns, and further comprising maintaining the central portion in a plane and bending the end turns out of the plane after the serpentine bends are formed.
 6. The method of claim 5, wherein compressing comprises compressing only the central portion of the serpentine configuration.
 7. The method of claim 6, further comprising combining multiple bundles of compacted Litz wire.
 8. The method of claim 1, further comprising combining multiple bundles of compacted Litz wire together to form the winding.
 9. The method of claim 8, wherein combining multiple bundles of compacted Litz wire comprises combining the bundles by at least one of: (a) layering; or (b) weaving.
 10. The method of claim 1, wherein forming the winding comprises forming an annular winding.
 11. The method of claim 10, wherein forming the winding comprises encasing the winding in epoxy comprising boron nitride.
 12. The method of claim 1, wherein forming the winding comprises encasing the winding in a thermally conductive epoxy.
 13. The method of claim 12, wherein encasing comprising encasing the winding in epoxy comprising boron nitride.
 14. A method for forming a motor winding comprising: a) bending a bundle of Litz wire into a serpentine configuration comprising central portions and end turns; b) compressing separately each of the central portions after bending the bundle of Litz wire into the serpentine configuration to form a bundle of compacted serpentine Litz wire; c) combining multiple bundles of compacted serpentine Litz wire after compressing the central portions of multiple bundles of Litz wires; and d) forming an annular stator winding comprising the multiple bundles of compacted serpentine Litz wire.
 15. The method of claim 14, wherein bending the bundle of Litz wire into a serpentine configuration comprises maintaining the central portions in a plane and bending the end turns out of the plane after the serpentine bends are formed.
 16. The method of claim 14, further comprising encasing the winding in a thermally conductive epoxy.
 17. The method of claim 16, wherein encasing the winding comprises encasing in epoxy comprising boron nitride.
 18. The method of claim 14, wherein combining multiple bundles of compacted serpentine Litz wire comprises combining the bundles of compacted serpentine Litz wire by at least one of: (a) layering; or (b) weaving.
 19. The method of claim 18, further comprising encasing the winding in epoxy comprising boron nitride.
 20. The method of claim 14, wherein forming the motor winding comprises forming a stator winding.
 21. The method of claim 14, wherein compressing comprises compressing only the central portions of the serpentine configuration.
 22. The method of claim 5, wherein the end turns are turn turned out of the plane so as to minimize a thickness of the Litz wire bundles in a central region of the winding.
 23. The method of claim 15, wherein the end turns are turn turned out of the plane so as to minimize a thickness of the Litz wire bundles in a central region of the annular stator winding. 